1. Field of the Invention
The present invention generally relates to speaker devices, and more particularly, to the structural designs of speaker devices.
2. Description of Related Art
Visual and acoustic means are two effective ways of communication. As a result, scientists and engineers have continued to develop components and systems for visual or acoustic applications. One acoustic application may include the use of speakers, including electro-acoustic speakers. Electro-acoustic speakers may be categorized as direct and indirect radiant speakers. Generally, speakers can also be roughly categorized, based on their operating theories, into dynamic speakers, piezoelectric speakers and electrostatic speakers. Dynamic or magnetic-membrane speakers have been frequently used because of their well-developed technologies and have dominated the speaker market. However, dynamic or magnetic-membrane speakers may have disadvantages due to their large sizes, making them less desirable for portable or smaller-sized consumer products or for other applications that have space constraints.
In contrast, piezoelectric speakers operate based on the piezoelectric effects of piezoelectric materials and rely the application of electrical fields to piezoelectric materials to drive sound-producing diaphragms or membranes. Piezoelectric speakers generally require less space and may have thin or planar designs. However, piezoelectric materials formed by sintering processes may be rigid and inflexible.
Additionally, electrostatic speakers are generally designed with two fixed electrode-plates having holes and holding a conductive membrane between the two plates for forming a capacitor. A DC voltage bias may be applied to the membrane, and an AC voltage may be applied to the two electrodes. The electrostatic force generated by the positive and negative fields may drive the conductive membrane to generate sound.
U.S. Pat. No. 3,894,199 illustrates an example of a conventional speaker design. Referring to FIG. 1, reproduced based on FIG. 2 of U.S. Pat. No. 3,894,199), an electro-acoustic transducer is used and includes two fixed electrodes 110 and 120 placed at the two sides of a membrane 130. Each of the two fixed electrodes 110 and 120 has holes for allowing the produced sound to pass through the electrodes. The membrane 130 is placed between the two electrodes 110 and 120. The electrodes 110 and 120 are connected to an AC signal or power supply 160 through a transformer 150. When the AC signal is applied to the electrodes 110 and 120, the variations in the voltage differences between the electrodes 110 and 120 cause the electrical field between the electrodes to vary, causing the membrane 130 to vibrate and produce sound.
The electro-acoustic transducer as illustrated may be bulky or expensive to make, and the design may provide limited efficiency in some applications. Therefore, it may be desirable to have alternative designs that may overcome, or be configured to overcome, one or more disadvantages associated with certain conventional designs of speakers.